This invention relates generally to the packaging of articles such as cans, bottles, and the like in paperboard trays and more particularly to a packaging machine for applying a sheet of film over the articles in the tray and bonding the film to the tray side walls to hold the articles in the tray.
Machines which package articles in open top paperboard trays by applying a sheet of film over the articles and bonding the film to the tray side walls are known in the prior art. While the film may be adhesively bonded to the tray side walls with these machines, a thermoplastic film is typically used which will bond to the tray side walls when the film is heated and pressed thereagainst. Also, the film used is typically heat shrinkable and the thusly formed package is subsequently heated to shrink the film and tightly lock the articles in the tray.
In these prior art machines, open top paperboard trays loaded with the articles to be packaged are moved along a prescribed path. As the trays are conveyed along the path, a sheet of thermoplastic film is dispersed over the articles in the tray and wrapped over the articles by a plurality of flight bars moving along an endless path. The tray with the articles therein is captivated between adjacent flight bars as the flight bars move along a portion of the endless path so that the flight bars force the film down between adjacent trays and press the film against the tray side walls. After the film is bonded to the tray side walls, the film between trays is severed to separate the packages from each other. Where the film is bonded to the trays using heat, the flight bars mount heating units thereon that press the film against the opposite sides of the tray and heat the film sufficiently to cause the film to adhere well to the tray.
U.S. Pat. No. 3,890,763 illustrates one type of machine for performing this packaging operation. In that machine, the flight bars are mounted at spaced apart positions between a pair of endless chains so that the chains move the flight bars around an endless path with a fixed spacing between the flight bars. This type machine is able to operate at relatively high speeds, however, the fixed spacing between the flight bars limits the machine to the handling of one size tray. Thus, in packaging operations using different size trays, this type machine has not been practical.
Another type machine is illustrated in U.S. Pat. No. 4,365,456 in which alternate flight bars are mounted between a first set of conveyor chains while the other flight bars are mounted between a second pair of conveyor chains where both the first and second sets of conveyor chains move along the same endless path. Since the first and second sets of conveyor chains can move relative to each other, the spacing between each set of adjacent flight bars can be varied. This allows the machine to accept different size trays for packaging. However, only one tray can be placed in compression at one time. This has limited the overall speed of the machine, especially where the film is welded to the tray side walls.